The present invention relates to a process for production of boehmite (also known as alpha-alumina monohydrate) in substantially pure form.
Boehmite is the mineral name of one of the oxide-hydroxides of aluminum and has the chemical formula AlO(OH). Processes for making boehmite are known in the art. However, each of the prior art processes suffers from one or more serious disadvantages making it less than entirely suitable for its intended purpose.
The three principal types of methods previously used to produce boehmite can be summarized as follows:
a. Hydrothermal--Treatment of aluminum trihydroxide at high temperature and steam pressure produces well-crystallized boehmite.
b. Neutralization--Aqueous solutions of aluminum salts such as aluminum chloride, aluminum sulfate and aluminum nitrate are neutralized by alkalis such as NaOH, KOH and NH.sub.4 OH, or aluminates such as sodium aluminate are neutralized by an acid (e.g. HCl or H.sub.2 SO.sub.4) or CO.sub.2 to produce gelatinous boehmite.
c. Hydrolysis--Organic aluminum compounds such as aluminum alkylates are hydrolyzed with water to produce gelatinous boehmite.
Boehmites produced by the latter two types of methods are generally of a gelatinous nature and are characterized by water contents that are significantly greater than stoichiometric (15.0 wt % for pure boehmite) and considerable broadening of the X-ray diffraction lines.
It is a principal objective of the present invention to produce boehmite directly by precipitation from a caustic aluminate liquor without requiring any hydrothermal conversion or chemical neutralization operation.
It is a related objective of the invention to provide a process for production of substantially pure boehmite that is more economical than prior art processes.
An advantage of the present invention is that the used aluminate solution from which boehmite has been precipitated can be reused for digestion of bauxite according to the Bayer process.
Additional objectives and advantages of the present invention will become apparent to persons skilled in the art from the following detailed description and drawings.